That's the easiest way to do it on a pre-964 car but I'm afraid 964 turbos have hydraulic brake boosters. There is no boost/vacuum source near the front of the car that I'm aware of.

You'll most likely have to run a small hose. Autometer makes a small plastic hose kit that works well. You can run it along the throttle cable and into the center tunnel. It'd be nice to put a coupling near where the throttle cable conduit connects. This would make it easier to remove engine/trans without cutting/splicing the hose later.

BTW, On the older cars I've used an early 944 brake booster ck valve that has that nipple made on to it. You can use an old early CIS(non-turbo) plastic fuel line to screw onto the back of the Clock style boost gauge that gives you a barbed fitting. Then all you need is some hose...